Nonaqueous electrolyte secondary batteries are used as power sources to drive electric power tools, electric vehicles (EVs), hybrid vehicles (HEVs and PHEVs) as well as in consumer applications, for example, mobile information terminals such as cellular phones, notebook personal computers, and smartphones and are expected to be more widely used. In particular, the prevalence of lithium ion secondary batteries has recently been further accelerated because of their high capacity and high power. Lithium ion secondary batteries are required to meet predetermined safety when subjected to an overcharge test.
In connection with this, PTL 1 discloses that the use of a positive electrode having a surface covered with a covering layer containing a phosphate compound and an oxide containing at least one of tungsten (W), molybdenum (Mo), and zirconium (Zr) inhibits heat generation at the time of overcharging to improve the safety.